Despite continuing beneficial technological advances, radio frequency communications systems will always be constrained within certain physical boundaries by limits on effective transmission range and will always be burdened with effects caused by various geographical and man-made barriers. The present invention specifically addresses these problems by providing the user with an improved multiple radio communications method and apparatus which automatically makes the best use of the equipment and available system resources to insure the highest quality communications at all times.
In both public safety organizations and commercial utility industries mobile radio users often find it necessary to communicate across regionally diverse areas, e.g., state police patrolling a large region of the state may need to remain in contact with city agencies when they are in the vicinity or a fire chief for a local municipality may be called in to support surrounding county agencies. Obviously, many similar situations exist. Different groups or agencies typically use the type of system and equipment that best suits their particular geographical and tactical needs. For example, a large coverage area UHF communications system may be suitable for a state governmental agency whereas a small 900 MHz trunked communications system would be more suitable for a city or municipal agency. Unfortunately, the geographic regions and specific communications needs of each agency or group are often vastly different. So when users of diverse type systems need to communicate to one another, the convenient solution of having them all communicate using the same trunked radio band or using a common conventional radio system is usually not feasible. (For the purpose of the present discussion, a "conventional" radio system--as opposed to a "trunked" system--is defined as frequency modulated (FM) and/or phase-modulated (PM) non-trunking RF communications system).
In the past there were no real solutions to this particular problem. Mobile communications users simply approached the problem by installing and using several different types of RF communications equipment. This resulted in multiple control panels, microphones, and hook switches vying for the typically very limited space available in a mobile environment. Moreover, the added conglomeration of devices still gave the user no insight as to which piece of radio equipment might operate the best at a present location. The user first had to try a radio to know whether or not it would provide satisfactory communications. The only radio known to at least partially address these problems is assignee's own Ericsson-GE ORION.TM. mobile radio, which combines two transceivers with a single control panel interface. This arrangement is known as a multiple radio apparatus or "multi-radio" and although it somewhat reduces equipment clutter it does nothing to help a mobile user know which transceiver is best to use at his current location.
Where a coordinated trunked communications system arrangement between differing agencies and/or commercial entities is not feasible, a lower cost alternative is to install at least one trunked system transceiver along with at least one conventional RF system transceiver in a "multi-radio" mobile equipment arrangement. In this way a mobile user can monitor, for example, a city agency's 800 MHz trunked site and then switch over to a wide area conventional RF system from the same control panel in order to communicate with a county or state agency that employs the wider coverage area system. Although such multi-radio arrangements may enable a user to hear communications on both transceivers, the user can only respond using one transceiver--i.e., the selected radio transceiver. Moreover, the conventional multi-radio systems require one to manually switch between the two transceivers.
Another current problem with mobile radio RF communications equipment is that sine one cannot physically "see" the radio system coverage boundaries, one has no way of knowing when he has reached the coverage limits of a particular communication system. Moreover, even when operating within the boundaries of a particular system there is no way of knowing when the existing transmission/reception conditions are no longer conductive toward providing high quality communications on that system. Even assuming the option to use other equipment or another type of RF communications system existed, a user would still not be able to determine exactly when it would be most advantageous to switch to the different system or if indeed that system would even be able to provide intelligible communications if the switch was made.
As an example, consider the case where a mobile RF communications user usually works within a large coverage region--for this example, a non-trunking "conventional" RF communications system--but also needs to remain in contact with users in a smaller coverage region which is trunked covered by a digital trunked system. In any digital trunked RF communications system, the quality of the transmission drops off as one leaves the primary coverage area. This results in calls that are unintelligible and places where trunked signaling cannot be decoded. Referring to FIG. 1A, a simplified example of primary (101) and marginal (102) coverage areas of a trunked communications system (100) is illustrated. Note that the area of marginal coverage, indicated by hatched region 102, is not necessarily uniform or consistent.
Typically, the audio quality of communications within a trunked communications system is better than that within the wide-area low-band, UHF or VHF conventional (i.e., non-trunked) system, but the geographical coverage area for most 800 MHz and 900 MHz trunked systems is much smaller. Therefore, if considering communications across two separate RF communications systems where one is a trunked system and the other is a non-trunked conventional RF communications system, the two of which have significantly different size coverage areas, it is usually the case that the smaller coverage area trunked system is contained wholly within the larger coverage area system. An example this type of situation is illustrated by FIG. 1B, where a trunked system 100 is shown contained within larger coverage area conventional RF communications system 110. Understandably, while travelling in the marginal coverage area a mobile user would not want to transmit on the trunked system if the audio quality has significantly decreased. However, if and when the signaling quality over the trunked communications system improves, it is usually preferable that the transmission take place on the trunked system.
With present multi-radio equipment, a user deciding to make a call over the trunked system must select the trunked system radio, "key-up" the transceiver, and just hope that one of the trunked system's base station would receive an intelligible signal. Typically, one would not know that the audio quality over the trunked system was bad until one received a call and could hear the quality of the received transmission. To address problems like these, and to solve the problem of trying to select which RF communications system and radio equipment to use when operating an outer perimeter of a system's coverage area (i.e., in the "marginal" area), the method and apparatus of the present invention provides an approach that is both automatic and transparent to the user. Basically, in the improved multi-radio of the present invention, an audio signal quality measurement is automatically obtained for each radio transceiver used in the apparatus and, on a continuing periodic basis, the quality currently obtainable on each transceiver is evaluated taking into account whether the evaluated transceiver is operating within a conventional or a trunked system. A determination is then made as to whether or not communications and control of the multi-radio apparatus should be switched over to a different transceiver.
In accordance with one aspect of the present invention, a multiple radio mobile transceiver apparatus having both a trunked system transceiver and a conventional RF transceiver is provided with a trunked/conventional auto-select capability (also called "E-C Autoset") that automatically selects the trunked system transceiver equipment for use whenever the audio quality on the trunked system is at or above a user-programmable minimum. A quality level preferred minimum is one chosen so as to provide the greatest coverage possible while preventing "ineffective" calls wherein user transmissions are too garbled to understand. The signal quality available on the trunked communications system is evaluated on a periodic basis whether or not a call is in progress. Whenever the signal quality degrades below the preset limit, the present invention automatically switches control to the transceiver equipment that operates using conventional RF communications. Moreover, the switching of control to the different transceiver equipment is accomplished electronically in a manner substantially transparent to the user. Thus, a mobile user is always provided with the ability to transmit (and receive) whether or not the quality of communications using the trunked RF system has degraded or become infeasible--for example, due to the user wandering outside the trunked system coverage area.
In accordance with another aspect of the present invention, a multiple radio mobile transceiver apparatus having at least two trunked system transceivers is provided with an "automatic radio roaming" feature that allows a user to freely roam between two (or more) trunked communications systems and it always selects the particular trunked system transceiver which provides the best audio quality. For example, when a mobile user is traveling near the limit of a coverage area corresponding to one trunked system, this auto-roaming feature of the present invention will cause the multi-radio to apparatus to automatically switch to another (albeit non-selected) trunked system transceiver whenever the measured audio quality on the selected transceiver degrades below a preprogrammed minimum.
Consequently, with the present invention, a mobile user needs no prior knowledge of the geographical coverage areas of the various RF communications systems available with the particular multi-radio apparatus. Moreover, a mobile user's concentration is not hampered by having to focus attention on operation of the radio equipment itself; to wit: switching between different communications systems and trying to determine whether he/she can be heard and understood. Instead, the transceiver selection is automated and overseeing the operation of the multiple radio equipment is greatly simplified. Moreover, for instances where a user would prefer to remain solely on the conventional system, the present invention has a transceiver autoselect disable feature that allows the user to disable the autoselecting of transceiver equipment for either a pre-programmed duration or until the user chooses to manually re-enable the automatic equipment selecting feature. In addition, the present invention also contemplates optional features such as providing the user with an audible indication whenever a "switch-over" to different radio transceiver equipment occurs.